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i'm a 12th grade student and our school has a safe competition, which means we need to build a safe that you can open with the laws of physics. we have a pendulum and we don't want it to move if someone is tilting the safe, so we want to make a "defense mechanism" against it, so i want to detect if someone moved the circuit and i have a mercury sensor. the circuit i want to build shuts off an other circuit powered by a 9 volt battery that contains a single electric motor for 3 seconds if someone moved it. how does the circuit looks like? i don't have any size constraints, i can store it and make it as big as needed.

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Not really enough information to answer. Depends on the circuit are you trying to shut off. eg - Are you looking to interrupt power to a circuit for 3s or just have a microcontroller do nothing for 3s. – spearson Mar 13 '12 at 18:30
interrupt power to a different circuit for 3s... – Someonation Mar 13 '12 at 18:41
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How much power are you talking about? voltage? size constraints? We need a lot more info. – Kellenjb Mar 13 '12 at 18:43
i want to interrupt a 9 volt battery powered circuit... what do you mean by size constraints? how many resistance is in the circuit? about 9 ohm. i'm sorry i don't know what information you need... i'm kind of a newbie – Someonation Mar 13 '12 at 18:49
By size constraints I mean do you have any limitation on physically how big the circuit can be. As far as power and voltage I am talking about what it is you are switching. The schematic would be very different for a 120VAC circuit then it would be for a 9V battery. Also would be very different if it is powering a motor or if it is powering a single LED. Please update your question with all of this type of info so that people don't have to read through comments to figure out what you are doing? – Kellenjb Mar 13 '12 at 19:01
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closed as not constructive by Kevin Vermeer Apr 12 '12 at 13:43

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1 Answer

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Instead of having a separate movement detector why not build it into the pendulum? A spring like this will short to the pendulum when movement is detected, but if the spring is supple enough will not hinder the movement. As long as the safe is being moved the 'switch' will be closed.

A spring based pendulum movement detector.

The detector circuit could be constructed from a 555 timer and a relay.

The 555 timer configured for retrigerable monostable operation:

The 555 can drive a small relay. Choose one a relay that is normally 'on' then when the circuit triggers it will turn off for the chosen time delay.

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